1. Field of the Invention
The present invention relates to the field of endodontics.
2. Description of Related Art
Root canal therapy has become well established as a viable clinical treatment to retain a tooth where the dental pulp has become painful, irreversibly inflamed, infected or necrotic (dead). The generally accepted method of performing a root canal is to drill an “access” opening into the root canal through the clinical crown of the tooth and then to remove the diseased or damaged pulpal tissues using small sharp files, rotary files, dental burs or drills. Once the pulpal tissue is removed, the root canal is treated with chemical agents to disinfect the canal, to remove any residual organic material and to remove what is commonly referred to as the debris “smear layer.” The cleaned root canal must then be “obturated,” which means that it is filled with an inert material that is capable of sealing the canal against the passage of fluids and microorganisms.
There are many strategies, materials and techniques that have successfully been used to obturate root canals. One method is simply to fill the root canal with an inert paste that is placed into the canal as a viscous liquid but sets hard after a period of working time. Historically, one of the most popular strategies is to use a solid core filler (sometimes called a “cone” or a “point”) which is surrounded by a viscous liquid sealer or paste. Like the method described above, the sealer is what is really providing the seal, but the solid core filler is necessary to hydraulically force the sealer around curves, into the small irregularities and accessory canals coming off the main root canal. The solid core filler also offers a convenient pathway back to the apex of the root canal should retreatment ever become necessary. These solid core fillers can be flexible, semi-rigid or rigid. The benchmark or gold standard for obturation that has emerged and dominated endodontics over the past century is to use a solid core filling of “gutta percha” and a self-setting sealer based on a formula made with zinc oxide and eugenol. Gutta percha was first introduced into dentistry by Edwin Truman as filling material in 1847 and was called Hill's stopping. Due to its thermoplastic properties, it rapidly found its way into popular use in endodontics by 1887 in the form of gutta percha points. In spite of the overall acceptance and clinical success of the gutta percha/sealer cement combination, many clinical studies have shown that the combination still leaks and diminishes the efficacy of the root canal seal. This has led to the continual search for easier and better materials to seal the root canal.
U.S. patent application Publication No. 2005/0069836 describes a new type of polyester based, thermoplastic obturation material that is able to fulfill all of the same functions as gutta percha but which also takes advantage of a much stronger chemical adhesion/bonding strategy to improve the seal. A commercial product believed to be embraced by this patent application is RESILON™ (polycaprolactone-based thermoplastic aliphatic polyester resin obturation material). In other words, RESILON™ can be thought of as a soft thermoplastic resin that is chemically bondable. This differs from gutta percha, which is based upon a naturally occurring latex rubber and is not chemically bondable. So, instead of simply cementing the point into the root canal, it is now possible to adhesively bond the point in and achieve a superb water tight, insoluble seal throughout the length of the canal.
What makes RESILON™ so important is that it takes advantage of the important scientific discipline referred to as “Adhesion Dentistry” or “bonding.” Bonding in dentistry has enjoyed explosive growth and improvement since its introduction. Through modern adhesion dentistry it is now possible to strongly link many different substrates to tooth structure, including resin composites, porcelains, and metals. However, RESILON™ marks the first real linking of endodontic obturation and adhesion bonding.
Adhesion bonding as well as the resin based restoratives in dentistry are almost all based upon compounds composed of monomeric precursors containing a C═C (carbon-carbon) double bond and which are catalyzed into linking and crosslinking into a solid, virtually insoluble polymeric structure. The composite resin restorative materials are generally highly filled with glass or silica particles to convert them into pastes, improve their strength and durability whereas the bonding agents are largely unfilled or sparsely filled, allowing them to remain as liquids. There are two main initiator systems used to convert the monomers into polymers. These are the photoinitiators and chemical initiators. This has allowed the creation of purely light cured resin composites and bonding agents (photoinitiated) as well as purely self/auto cure resin composites and bonding agents. There are also hybrid resin composites and adhesives which contain both initiator systems and are referred to as “dual cured.” The attachment of these polymeric restorative and adhesive materials to tooth structure requires a special chemical treatment of the tooth surface called “etching.” In the process of etching, a weak acid is applied to the tooth which extracts some of the calcium hydroxyapatite salts that mineralizes both enamel and dentin. The resultant surface is able to adhere to the adhesive products much more efficiently.
A number of manufacturers currently utilize RESILON™ in their root canal protocols. EPIPHANY™ and REALSEAL™ utilize solid core obturators made entirely of RESILON™. To bond these obturators into the canal, the dentist first irrigates the canal with NaOCl (sodium hypochlorite). This clears the canal of organic debris and disinfects. EDTA (ethylene diamine tetraacetic acid) is then used to neutralize the NaOCl and demineralize the walls of the root canal. This is followed by the placement of an adhesive primer and then the placement of a dual cured resin based endo sealer. The RESILON™ point is seated into the sealer and stabilized by light curing from the crown side. After a period of time, the self-curing/autocuring chemistry of the sealer will activate allowing the sealer deep in the canal to set fully. The result is a total adhesive seal from the apex of the root to the crown with a central core of RESILON™.
INNOENDO™ and SIMPLIFILL™ are carrier based obturators. SIMPLIFILL™ utilizes a metal rod carrier to push a small plug of RESILON™ deep into the canal. The carrier rod is then twisted and removed and the remaining space in the canal is backfilled with RESILON™ points. INNOENDO™ utilizes a fiberglass carrier which holds a small tip of RESILON™ on the end. As the INNOENDO™ is seated into the canal the RESILON™ is forced down deep into the canal all the way to the apex of the root. However, in INNOENDO™, the carrier is left in the root canal and forms the seal in the upper coronal part of the canal. Since all manufacturers are basically licensing the RESILON™ Technology from Resilon Research LLC, they all use the very same RESILON™ material and variations of the same resin based primers and sealers. So for INNOENDO™ and SIMPLIFILL™ you are also required to irrigate the tooth with NaOCl and EDTA, followed by an adhesive primer and sealer application.
Progress has allowed the development of what have been described as “self-etching dental adhesives” and “self-adhesive resin composites.” These products have an acidic formula that allows them to bond to tooth structure without the necessity of pretreating the tooth with a weak acid. This permits the dentist to save time during the clinical treatment. Most recently, there have been introduced into the marketplace several “self adhesive resin cement” products. These products allow for a much more reliable, higher strength adhesive bonding like attachment of dental restorations such as dental crowns and bridges, dental inlays and onlays and laminate veneers to tooth structure. Dentists like these products because they eliminate the extra etching step but can still maintain high bond strengths of resin bonding. Commercial examples of the self adhesive resin based cements include UNICEM™ (3M/ESPE), MAXCEM™ (Kerr Dental) and EMBRACE WETBOND™ (Pulpdent), the latter of which is believed embraced by U.S. Pat. No. 6,797,767.
Thus far, these “self-etching dental adhesives” and “self-adhesive resin composites” have not been used in endodontics, and particularly not as sealers for root canal obturations.
In spite of improvements resulting from the use of RESILON™, further improvements in seal strength and other properties are needed.